388 
GEOLOGY AND GEOGRAPHY 
mer, and the components of potash and alumina of the 
latter, is too well-known to require more than a passing 
notice here. Based upon this data, my attention has been par¬ 
ticularly directed to the decomposition of those rocks in which 
the above minerals form a part, and although the homogene¬ 
ous nature of the deposits formed by their decomposition 
does not admit of a clear insight into their mechanical con¬ 
struction, it may nevertheless be concluded, that laterite in 
all its modifications, is but the resultant of such decomposi¬ 
tion. This operation is distinctly traceable in a decomposing 
gneiss rock forming the overlying strata on the coast of this 
place, (Amherst) ; the atmospheric influence has penetrated 
the rock to a considerable distance below the surface, giving 
it a mottled appearance, but on any new abrasion of the bank 
by the action of the waves of the S.W. monsoon, the strata are 
seen distinctly laminated, with the hornblende and felspar in 
a high state of decomposition ; their complete reduction is 
effected in a short period after exposure to the heavy rains 
of the monsoon which percolate the mass and precipitate it to 
the base, where the - undecomposed quartz finds a matrix, 
which, under a subsequent chemical process brought into 
operation by the combined influence of the atmospheric 
action and the oxide of iron of the hornblende, becomes 
indurated and compact or cellular, according to the ingre¬ 
dients of the rocks, from the decomposition of which they 
were formed. Laterite occcurs very generally throughout 
the Provinces, accompanying the old red sandstone and 
the formations of the primary order before mentioned ; it is 
seen cropping out at the surface in isolated masses which 
are highly ferruginous and indurated ; it also occurs loosely 
aggregated and permeated by quartz veins of I to 3 inches in 
thickness.* 
* One species of lateritic rock originates in the mode explained by our able 
contributor, and it is natural to conclude with respect to lateritic rocks generally, 
that when the results are so nearly identical in appearance, the process must 
have been the Bame Mr Riley's explanation we believe to be perfectly cor¬ 
rect for the laterites which he describes ; and many lateritic tracts in India, as 
well as some of those which we have examined in the southern part of the Ma¬ 
la; Peninsula, have been produced in the same mode. The extension of this 
explanation to all other rocks of a lateritic aspect, if it cau be properly called an 
error, is one which oux contributor shares with many Indian geological writers, 
amongst whom Dr Clarke has most elaborately applied it to the laterites of the 
Indian Peninsula (Madras Journal, 1838, p. p. 334-346), In reality the error 
is not in the explanation, but in the assumption that all laterites must have the 
same origin This assumption, and much of the conflict of opinion respecting 
laterite, is traceable to the remarkable property which iron possesses in peroxi- 
diaing, of assimilating the external aspect, and even to a certain extent the struc¬ 
ture, of the rocks in which it is disseminated, however they may hare differed 
